Tooth set for a hydraulic machine

ABSTRACT

The invention concerns a tooth set for a hydraulic machine, particularly a steering unit, with a toothed ring, having teeth, which are formed by means of inserts arranged in a housing, and a gear wheel arranged inside the toothed ring. It is endeavoured to simplify the production of such a tooth set. For this purpose, each inset ( 10 ) has, at least at its ends, a plate-like shape and the ends are fixed in the housing ( 11 ) in corresponding slots ( 17, 18 ).

[0001] The invention concerns a tooth set for a hydraulic machine,particularly a steering unit, with a toothed ring, having teeth, whichare formed by means of inserts arranged in a housing, and a gear wheelarranged inside the toothed ring.

[0002] Such a machine is known from U.S. Pat. No. 3,289,602.

[0003] In the following, the invention is described on the basis ofso-called “orbit” machines, in which the gear wheel has one tooth lessthan the toothed ring and the gear wheel orbits and rotates in thetoothed ring. This movement causes the teeth of the gear wheel and theteeth of the toothed ring to form limitation spots for individualpressure pockets, each pressure pocket being alternatingly exposed topressure and relieved during motor operation. During motor operation thesituation is directly reversed: Pressure pockets with a volume, which isreduced at a further movement of the gear wheel, are connected with apressure connection, whereas pressure pockets, whose volume increases atthe further movement, are connected with a suction connection. Theefficiency of such machines is determined by, among other things, theinner tightness, that is, by the reliability, with which the individualpressure chambers are sealed against each other at the contact spots ofthe teeth of gear wheel and toothed ring. The same problems also applyfor other tooth sets for hydraulic machines, in which a sealing betweenpressure chambers is also required, for example gerotor machines.

[0004] The tightness can be improved in that very narrow fits areprovided between the toothed ring and the gear wheel. However, thiscauses that the frictional losses get very high, and that a substantialwear occurs. Additionally, the production of such tooth sets isrelatively expensive.

[0005] Thus, it is proposed in U.S. Pat. No. 3,289,602, mentioned in theintroduction, to form the teeth of the toothed ring from small tubes,which are supported in corresponding bores in the housing. In thisconnection, the tubes, or at least their surfaces, can be made of a veryhard material, while the housing can be made of a softer material, whichis consequently cheaper to work. In an alternative embodiment the tubesare replaced by cross-sectionally square bars, which are rounded in thearea of the teeth and supported in the housing with a play, so thattheir angle position in relation to the gear wheel changes in dependenceof the actually ruling forces. The same adjustment opportunity is alsoavailable for the tubes.

[0006] The invention is based on the task of simplifying the productionof a tooth set.

[0007] With a tooth set as mentioned in the introduction, this task issolved in that at least at its ends each insert has a plate-like shapeand that the ends are fixed in the housing in corresponding slots.

[0008] This embodiment has the advantage that the inserts can besubstantially simplified, and still be retained reliably in the housing.The material of the inserts and the material of the housing can bechosen independently of each other, the material of the inserts beingchosen with a view to wear resistance and a good cooperation with theteeth of the gear wheel. The housing only has to be stable enough tostand the ruling pressures. A resistance towards the wear of the gearwheel, however, is no longer required. As now, the efforts can beconcentrated on inserts, on which the “bearing surface”, that is, thearea along which the teeth of the gear wheel are rubbing, is clearlydefined and thus limited, the cost for the material will be kept low.The plate-like shape of the ends gives surface sections, through whichthe inserts are retained radially and in the circumferential direction,without requiring an expensive working of the housing.

[0009] Preferably, the insert is made of a bent plate. Such a plate iseasily produced, and in this connection the term “bent” refers to thefinal state, that is, the curve shape can also be made in other waysthan by means of the production process of bending. Through a bendingprocess, however, the insert can be provided with a certain pretension,so that a certain internal tension helps retaining it in the slots inthe housing.

[0010] Preferably, the insert is made of spring steel. Spring steel is arelatively hard material, so that the “teeth” or the wearing surfaces ofthe teeth consist of a correspondingly resistant material. Spring steelis a relatively inexpensive material. The surface of spring steel needspractically no further working, like for example a hardening, whichsimplifies the production further.

[0011] Advantageously, the slots are directed so that they form apredetermined angle to the radial direction. Thus, the slots can beinclined somewhat in the tangential direction, so that the insertion ofthe plate-like ends is facilitated. For example, the slots can have adirection, which corresponds to the tangent of a circularly bent toothin the spot, where the insert projects into the housing.

[0012] Preferably, at each insert the housing has a radially inwardprojecting boss, which fills a space surrounded by the bent plate. Thus,the housing supports the tooth, that is, the bent plate. Or, to put itsimply, the tooth is still formed by the housing, the bearing surfacebeing covered by the insert. Thus, the toothed ring can be produced veryaccurately, without requiring the use of expensive materials. However, avery good wear resistance is still obtained.

[0013] In an alternative embodiment a gap may exist between the bentplate and the housing. No longer being supported by the housing, thebent plate is therefore a little flexible. This gives each tooth a smallflexibility or elasticity, so that a pairing grinding, which is used foralmost all tooth sets today, can be avoided. The flexibility of such atooth is extremely small. At the highest, it is in the μm-area. However,it is sufficient to permit a substantial reduction of the accuracy ofthe fit between gear wheel and toothed ring.

[0014] Preferably, the housing-side limiting wall of the gap is formedby a circumferential cylinder surface, whose diameter corresponds to theinner diameter of the housing. Additionally to the flexibility orelasticity of the tooth, this gives an additional production advantage.The housing can be made as a simple cylinder ring, which is very easilyproduced, for example by turning. The slots for adopting the insertmerely have to be made in the inside of this cylinder ring.

[0015] Preferably, the gap is filled with a compressible material. Sucha material can, for example, be rubber or another elastomer material.Thus, on the one hand, the resilience of the tooth is maintained. On theother hand, however, the tooth is in some way supported from the inside.Additionally, this embodiment has the advantage that the insert can beprestressed from the inside, that is, from the housing, so that theinsert is held firmly in the housing already then, when the gear wheelis not yet mounted.

[0016] In an alternative embodiment, the insert can be made of aprofile, whose cross section is formed by the combination of a circlesection and an oppositely bent rib, which projects sideward over thecircle section. In this case, the plate-like embodiment of the insertcan only be recognised at its ends in the circumferential direction.Otherwise, the insert is again a massive or, if desired, also a groovedbody, at least a body, which obtains a three-dimensional extension notonly through bending. However, also here the plate-like ends serve asholders for the teeth in the housing. Such inserts are also relativelyeasy to produce. For example, such inserts can be cut off from aprofile. The inserts can be made of steel. Here, an additional advantageof these and the abovementioned inserts appears. The simple change ofthe length, which must be made simultaneously with a change of the axiallength of housing and gear wheel, the output of the tooth set can bechanged.

[0017] In this connection, it is preferred that the surface of thecircle section is hardened. The other parts of the insert can remainunhardened. This embodiment firstly simplifies the production andsecondly improves the operating behaviour.

[0018] Preferably, the inserts project axially over the front side on atleast one front side, and the front side is covered by a plate, whichhas openings corresponding to the inserts. Thus, the front side sealingbetween the teeth of the toothed ring is displaced from the contactsurface between the plate and the toothed ring into the inside of theplate. This gives substantial advantages. Thus, it is no longernecessary for the inserts to be plane parallel with the front side ofthe housing after mounting. Accordingly, a working with this purpose canbe avoided. In the area of the teeth of the toothed ring, the tooth setis still “tight”, when, for example, the corresponding front side of theinsert forms a small angle with the surface, or the insert has a certainroughness on the surface. Accordingly, the inserts can simply be cut offfrom a straight profile, for example by means of sawing. Thus, theinserts are already usable. A sealing is much more easily procured withan inserted part than with a merely bearing part.

[0019] In this connection it is preferred that the depth of the openingsis larger than the projecting of the inserts. Thus, also the accuracywhen cutting off and mounting the inserts can be reduced.

[0020] Preferably, in relation to the bearing surface, the housing ismade of a soft material. A soft material is easier to work. It isusually cheaper. It only has to be sufficiently pressure resistant toadopt the pressures occurring during operation. There are no furtherrequirements. Such a pressure resistance can, for example, be obtainedin that on its radial outside the housing is wound with tighteningstraps, for example, fibre-reinforced tightening straps.

[0021] In a particularly preferred embodiment, it is provided that thesurface of the teeth is smoothened in parallel to the movement directionof the gear wheel. Such an embodiment is only possible through the useof separate teeth in the toothed ring, as here the smoothing tool can beapplied so that the smoothing tracks extend in the same direction, inwhich later also the gear wheel will pass the bearing surface of theindividual teeth. In toothed rings, which are made in one piece, thesmoothing tracks always extend perpendicularly to this direction, whichgives noise during operation, which is to some extent disturbing.

[0022] In the following, the invention is described in detail on thebasis of preferred embodiments in connection with the drawings, showing:

[0023]FIG. 1 a schematic view of a tooth set

[0024]FIG. 2 a section of a toothed ring of the tooth set

[0025]FIG. 3 a perspective view of a tooth according to FIG. 2

[0026]FIG. 4 a section IV-IV according to FIG. 3

[0027]FIG. 5 a top-view of the tooth

[0028]FIG. 6 a perspective view of a modified embodiment

[0029]FIG. 7 a section VII-VII according to FIG. 6

[0030]FIG. 8 a top view of a tooth according to FIG. 6

[0031]FIG. 9 a further embodiment

[0032]FIG. 1 shows a tooth set 1 with a toothed ring 2 and a gear wheel3. The gear wheel 3 has one tooth less than the toothed ring 2. Thecentre 4 of the gear wheel 3 is offset in relation to the centre 5 ofthe toothed ring, so that the gear wheel 3, when rotating in thedirection of the arrow 6, rotates and orbits in the toothed ring. Such atooth set can be used either as a pump or as a motor. In thisconnection, pressure pockets 7 are formed between the gear wheel 3 andthe toothed ring 2, which pressure pockets 7 are either pressurised orreleased in dependence of the desired function. Such tooth sets 1 arecommonly known. For further information, see, for example, U.S. Pat. No.3,289,602.

[0033] Neighbouring pressure pockets 7 are sealed against each other viaa contact point 8 between the toothed ring 2 and the gear wheel 3. Thisrequires that the gear wheel 3 bears on the toothed ring with a certainpressure. Of course, an embodiment like this causes a certain wear,which reduces the life, when no counter-measures are taken. Such acounter-measure, which is easily realised, is explained in thefollowing.

[0034]FIG. 2 shows a section of the toothed ring 2 with a tooth 9, whichis covered on the surface facing the gear wheel 3, not shown in detail,with an insert 10 of spring steel. This insert 10 is inserted in ahousing 11, as shown in the FIGS. 3 to 5. Thus, the housing can be madeof a relatively soft material, for example aluminium. Such a material iseasy to work. If the hydraulic pressures should make it necessary, thehousing 11 can be reinforced from the outside by means of tighteningstraps, for example fibre-reinforced straps or straps of spring steel.Otherwise, the housing 11 can be relatively “thin”, that is, have arelatively small radial extension.

[0035] Spring steel, on the other hand, is a relatively hard material,which only shows small signs of wear, even with a heavy friction. Thesurfaces of spring steel almost need no further treatment. Particularly,in most cases, a hardening is not required. Normally, the surface of thespring steel insert 10 only has to be smoothed. However, in thisconnection, the smoothing tracks can have a direction causing them to beparallel to the sliding or movement direction of the gear wheel 3 acrossthe insert 10, that is, substantially in the circumferential direction.The smoothing and polishing, if any, can be made for as long as theinsert 10 is still outside the housing 11. The insert 10 can be smoothedand perhaps polished already when the spring steel has not yet beenbent. A smoothing and polishing can, however, also be made withoutproblems in the bent state.

[0036]FIG. 3 shows the tooth 9 in the housing 11 in a perspective view.From this it can be seen that the insert 10 projects in the radialdirection over the front side of the housing 11. This is also shown inFIG. 4. A cover 12, 13 then has a corresponding opening 14, 15, that is,a groove extending in a curve-shape, in which the projection of theinsert 10 can engage. For reasons of clarification, FIG. 4 shows thehousing 11 and the covers 12, 13 and the insert 10, respectively, withdistances between them. These distances do not exist in reality. On thecontrary, the individual parts fit each other “seamlessly”. Oneexception from this is that the depth of the grooves 14, 15 is largerthan the projection of the insert 10 over the housing 11. Therefore, theinsert 10 can simply be cut off to the desired length from a springsteel profile, in the most simple case even from a spring steel band. Inthis connection, the required accuracy only plays a minor part, as longas it is ensured that the insert 10 goes deep enough into the plates 12,13 to provide the corresponding sealing. Particularly, the front sidesof the insert 10 no longer have to end together with the front side ofthe housing 11 or to be smoothed to be plane parallel to the front sideof the housing 11. On the contrary, the sealing appears on bearingsurface 16 of the insert 10.

[0037] For the adoption of the insert 10, the housing has slots 17, 18in the circumferential direction on both sides of the tooth 9, theinsert 10 being inserted in said slots. Expediently, the insert isinserted in the slots 17, 18 in the axial direction, which simplifiesthe production substantially. However, in connection with the mounting,it is also possible to bend the insert 10 more than required and then toinsert it in the slots 17, 18. The insert 10 is then held in the housingwith a certain prestress. The inserts 10 can also be poured in. Theslots 17, 18 are not directed exactly to the radial direction, butenclose an angle α with this radial direction. Thus, they have a smallcomponent in the circumferential direction. An extension 20 of one wallof the slot 18 corresponds to the tangent of the insert, where theinsert 10 goes into the housing 11.

[0038] As stated above, the insert 10 can be made by bending a springsteel band. However, it is also possible to use a profile, which isalready curved, from which the corresponding inserts 10 are cut off.Preferably, the bearing surface 16 of the insert 10 should correspond toa section of an outer cylinder surface, at least in the area in whichlater a contact with the teeth of the gear wheel 3 will take place.

[0039] The FIGS. 6 to 8 show a modified embodiment. While in theembodiment according to the FIGS. 3 to 5 the housing 11 is made as anannulus with radially inward projecting teeth 9, the housing 11′ has noteeth. Otherwise, the embodiment of the insert 10 is unchanged. Theinsert 10 is still inserted in the slots 17, 18. However, the productionof the housing 11′ is substantially simplified. An annulus with thedesired radial thickness can simply be produce and inserted in the slots17, 18. Thus, the housing 11′ is ready to receive the insert 10. Asshown in FIG. 7, it is possible, in this case, for the insert 10 to havethe same axial extension than the housing 11′ (which is also possible inthe embodiment according to FIGS. 3 to 5).

[0040] Between the housing 11′ and the insert 10 there is a hollowspace. This hollow space can be left open. However, it can also, asshown in FIG. 7, be filled with a compressible material for examplerubber or another elastomer. In both cases, the flexibility orelasticity of the tooth formed by the insert 10 is increased. Also whenthe movements made possible by this are only in the μm range, thisembodiment with reduced accuracy provides a substantially improved fit.In particular, the pairing smoothing of gear wheel 3 and toothed ring 2can be avoided.

[0041] In the embodiments in FIGS. 2 to 8 the insert 10 is simply a bentplate, which is inserted in the slots 17, 18. The plate can also be madeof an originally smooth or flat material.

[0042]FIG. 9 shows a modified embodiment of a toothed ring 3′ withinserts 22, having in advance a three-dimensional shape. These insertscan, for example, be cut off from a corresponding profile. From across-sectional view, this shape is formed by a bent plate 23 and acylinder section 24, the separating line 25 between these two componentsbeing, however, only fictive or imagined. The ends 26, 27 of the plate23 are fixed in corresponding slots 28, 29 in the housing 30. In thiscase, the housing 30 can be made, for example, by sintering, to createthe slots 28, 29. However, it is also possible to cast the housingaround the inserts 23.

[0043] The inserts 22 can also be made of steel, particularly springsteel. Also their surfaces can be smoothed accordingly.

1. Tooth set for a hydraulic machine, particularly a steering unit, witha toothed ring, having teeth, which are formed by means of insertsarranged in a housing, and a gear wheel arranged inside the toothedring, characterised in that at least at its ends (26, 27) each insert(10, 22) has a plate-like shape and that the ends (26, 27) are fixed inthe housing (11, 11′, 30) in corresponding slots (17, 18; 28, 29). 2.Tooth set according to claim 1, characterised in that the insert (10) ismade of a bent plate.
 3. Tooth set according to claim 1 or 2,characterised in that the insert (10, 22) is made of spring steel. 4.Tooth set according to one of the claims 1 to 3, characterised in thatthe slots (17, 18; 28, 29) are directed so that they form apredetermined angle to the radial direction (19).
 5. Tooth set accordingto one of the claims 2 to 4, characterised in that at each insert thehousing (11) has a radially inward projecting boss (9), which fills aspace surrounded by the bent plate (10).
 6. Tooth set according to oneof the claims 2 to 4, characterised in that a gap exists between thebent plate (10) and the housing (11′).
 7. Tooth set according to claim6, characterised in that the housing-side limiting wall of the gap isformed by a circumferential cylinder surface, whose diameter correspondsto the inner diameter of the housing (11′).
 8. Tooth set according toclaim 6 or 7, characterised in that the gap is filled with acompressible material (21).
 9. Tooth set according to claim 1,characterised in that the insert (22) is made of a profile, whose crosssection is formed by the combination of a circle section (24) and anoppositely bent rib (23), which projects sideward over the circlesection (24).
 10. Tooth set according to claim 9, characterised in thatthe surface of the circle section (24) is hardened.
 11. Tooth setaccording to one of the claims 1 to 10, characterised in that theinserts (10, 22) project axially over the front side on at least onefront side, and the front side is covered by a plate (12, 13), which hasopenings (14, 15) corresponding to the inserts.
 12. Tooth set accordingto claim 11, characterised in that the depth of the openings (14, 15) islarger than the projecting of the inserts (10).
 13. Tooth set accordingto one of the claims 1 to 12, characterised in that in relation to thebearing surface (16), the housing (11, 11′) is made of a soft material.14. Tooth set according to one of the claims 1 to 12, characterised inthat the surface of the teeth is smoothened in parallel to the movementdirection of the gear wheel (3).